1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus, and more particularly to such an apparatus for picking up an objective field by a solid-state image sensor and dividing the signal charges of an image representative of the field picked up into those of a plurality of sub-images to be outputted via a corresponding plurality of output circuits at a high transfer rate. The present invention also relates to a method for use in such a solid-state image pickup apparatus.
2. Description of the Background Art
Some of the conventional solid-state image pickup apparatuses have a solid-state image sensor of which the entire area of the imaging surface or photosensitive cell array is divided into a plurality of sub-areas in terms of reading out optical signal charges. The image signals representing the picked-up optical image of an objective field are rapidly read out as a plurality of sub-image signals respectively corresponding to the sub-areas. The image signals are then rapidly outputted via a plurality of output circuits. The output circuits include a preamplifier such as a floating diffusion amplifier (FDA).
The signals of sub-images are outputted separately from each other via correspondingly different output circuits. The output circuits have the amplifier characteristics thereof which may often be different or offset from each other. The picked-up sub-images thus have differences in characteristics of, e.g. offset, linearity, sensitivity, and dark noise, from each other. An entire frame of image made of the sub-images combined with each other may often have a dividing straight line in between which is clearly visible due to the colors, noise components and the like disadvantageously different there across.
Japanese patent laid-open publication No. 2002-125149 discloses an image pickup apparatus for obtaining respective average values of pixel data outputted from predetermined areas of the left, right, and left and right half imaging surfaces of an image sensor, the average values being in turn used to correct the imbalance in two outputs from the image sensor.
Japanese patent laid-open publication No. 2003-298950 discloses an image pickup apparatus in which a controller determines, for each channel, the level difference of two pilot signals from a solid-state image sensor, and a gain corrector corrects the level so that the level difference between the pilot signals on two channels are equal, thus increasing the detection accuracy of the input pilot signal and improving the level correction accuracy between the channels.
Japanese patent laid-open publication No. 2003-304454 discloses an image pickup apparatus in which the difference between a VOB signal level around the center of the image frame and the average of optical black (OB) signal levels in two horizontal optical black areas is divided by the number of the pixels of a horizontal line in the two divided imaging areas to provide the result of the calculation as a correction value. To or from the video signal, optical black signal, and pilot signal, the correction value is then added or subtracted for every predetermined number of horizontal pixels of the input signal for each channel, thus almost equalizing the output level characteristics of the divided imaging areas of the solid-state image sensor.
Japanese patent laid-open publication No. 2004-336244 teaches a correction apparatus that includes a gain adjustment means that adjusts levels of a plurality of image signals from a corresponding plurality of output circuits of the image sensor, and a microcomputer adapted to determine a correction coefficient for decreasing the level difference between a plurality of image signals based on temperature information, the gain adjustment means using the correction coefficient to decrease the level difference between the image signals, thereby correcting the image signals.
The conventional solid-state image pickup apparatuses output data of the sub-images via the output circuits distinct from each other, and correct the data of sub-images in dependence upon the outputted sub-images. The conventional apparatuses cannot determine which one of the sub-image signals is accurate or which one of the output circuits is defective. The correction thus cannot be done with reference to accurate one of the sub-images.